Lighting equipment that uses light-emitting diodes has been put to practical use in recent years. When light-emitting diodes are used as the light source for the purpose of lighting, a combination of light-emitting diodes that emit light of multiple different colors (usually red (R), green (G), and blue (B)) is generally used because it is easy to control color tone, color reproducibility is excellent, etc. White lighting with good color rendering properties is obtained by mixing light of these different wavelengths.
On the other hand, optical communication using this type of lighting equipment has been attempted (refer to JP Unexamined Patent Application (Kokai) 2004-147,063). By means of this system, the lighting equipment that is used for indoor lighting comprises multiple light-emitting diodes. The multiple light-emitting diodes usually emit light of different colors to provide light for lighting that is a mixture of the colors of emitted light while at the same time provide signal light that has been modulated by a predetermined formula. Terminals disposed under the illuminated environment receive this light and extract the modulated information signals.
It is necessary to maintain the component of each emission color at the appropriate ratio in order to maintain white light for lighting that has sufficient color rendering properties. Consequently, a modulation of the light for lighting should be conducted while minimizing the effect on human vision. Moreover, it is also necessary to guarantee sufficient illumination for lighting when the light source is used for the purpose of lighting.
Nevertheless, by means of conventional modulation forms, it is difficult to maintain color rendering properties or color temperature with this type of system and perform high-speed base band signal transmission at the same time. That is, when large volumes of information are subjected to signal transmission by conventional intensity modulation, there is an effect on the illumination of the lighting, or the shade of the color of the mixed light. Therefore, an object of the present invention is to provide a communication system that uses light for lighting, as well as lighting equipment and terminal equipment used in the same, with which high-speed signal transmission is possible.
The present invention provides a novel optical communication system and lighting equipment used therein in order to solve the above-mentioned problems. Code division multiple access communication is performed by this optical communication system and lighting equipment.